A number of mutually different drying sections intended for paper machines are known to the art, the majority of which sections incorporate a cylinder dryer and/or a fan dryer with which to effect drying of the web. It has long been known that, when drying a paper web in the drying section of a paper machine, the web tends to shrink in both the longitudinal and transverse directions thereof
It is also known that shrinking of the web in its transport direction or machine direction can be controlled by driving mutually adjacent drying means in the drying section at different speeds. It is also known that improved values, or an improved index, can be achieved with regard to the strength properties of paper, by controlled reduction of shrinkage of the paper web in its axial or transport direction.
It is also known that controlled reduction in web shrinkage transversely to the web axis cannot be achieved in dryers of the aforesaid kind.
It has been shown, however, that a small force of certain magnitude acts across the whole width of the paper web, from the centre of the web outwards, as a result of the friction prevailing between the peripheral surface of a drying cylinder and the web. In connection with the known art there is described and illustrated in U.S. Pat. No. 3,650,043 an arrangement designed to stabilize a dried paper web by blowing air thereonto in a manner to stretch the web.
U.S. Pat. No. 3,452,447 also describes an arrangement for stabilizing a dried paper web by blowing streams of air thereonto so that the web is stretched.
It should be emphasized here that these paper webs have a dryness in excess of 75% and preferably about 95%.